Electronic devices typically produce electrical signals that are driven by transistors or other types of switches. The power that can be driven by transistors in these signals is limited, and various techniques are used to increase power in an electronic device. One of these techniques is to divide an amplifier generating a high power signal into a number of segments. The outputs of the amplifier segments are combined to increase the overall output power in the signal. Thus, multiple segments in a segmented amplifier work in tandem to generate an electrical signal at a higher power than a single amplifier working alone.
In some systems, segmented amplifiers are designed to produce variable output power by activating a selected subset of the amplifier segments. To generate a full power signal, all amplifier segments are activated, but if less than full power is needed, some of the amplifier segments are activated and others are not. This type of selective activation can lead to unequal degradation of the transistors in the amplifier segments over the lifetime of the transistors, causing mismatches between segments. For example, when the drains of deep sub-micron CMOS transistors experience large signal swings as is often the case in amplifier transistors, they can experience hot-carrier induced parametric degradation and oxide breakdown. When some amplifier segments are used much more frequently than other segments, transistors in the most used segments are degraded faster than transistors in the least used segments. The resulting mismatch between transistors in segmented amplifiers can cause phase shifts between outputs and much lower total output power due to individual load mismatch.